1. Field of the Invention
The present invention relates to a method for the preparation of a .beta.-anilino-.beta.-hydrazinoacrylate which comprises reacting a .beta.-anilino-.beta.-alkoxyacrylate with a hydrazine, and to a method for preparation of a 3-anilino-5-pyrazolone using the .beta.-anilino-.beta.-hydrazinoacrylate.
2. Description of the Prior Art
3-Anilino-5-pyrazolones are valuable compounds useful as intermediates of dyes and as photographic magenta color-forming couplers. Of the 3-anilino-5-pyrazolones, compounds which have a substituent such as a halogen atom, an alkyl group or an alkoxy group in the 2-position of the 3-anilino group and a hydrophobic group containing 6 or more carbon atoms on the 3-anilino group are particularly useful for magenta color-forming couplers in view of their superior photographic properties.
Several methods of preparing 3-anilino-5-pyrazolones have heretofore been provided. However these methods have defects in that the reaction steps are complicated, the yields of the products are low, expensive agents are used in the reaction, and the like. Of these methods, the method described in British Pat. No. 1,129,333 in which a .beta.-anilino-.beta.-alkoxyacrylate is reacted with a hydrazine in the presence of an alkali metal alkoxide is the most useful, but the yields of the product are still unsatisfactory. In particular, when the method is applied to the preparation of 5-pyrazolones having a hydrophobic group on the anilino group as described above, the desired 3-anilino-5-pyrazolones can not be obtained or is obtained in extremely low yields.
The reactions of conventional methods have now been investigated in great detail and it has been found that when a .beta.-anilino-.beta.-alkoxyacrylate is reacted with a hydrazine, a subsidiary reaction in which the anilino group attached to the .beta.-position of the .beta.-anilino-.beta.-alkoxyacrylate is released proceeds simultaneously to lead to the formation of a complicated reaction mixture. As a result, when such is followed with a ring closing reaction in which an alkali and the like is added to the reaction mixture, the desired 3-anilino-5-pyrazolone is obtained in very low purity and poor yields. In particular, when a compound in which the anilino group has a hydrophobic group is used, isolation and purification of the desired compound is extremely difficult and therefore almost none of the desired compound can be obtained.